JPH06188017A - Phosphoric acid type fuel battery power generation plant - Google Patents

Abstract

PURPOSE:To provide a fuel battery power generation plant for minimizing the volume change in phosphoric acid in a fuel battery main body during starting as well as stopping operation. CONSTITUTION:A fuel and an oxidant are respectively guided to the anode electrode 2 and the cathode electrode 3 of a fuel battery main body 1. An anode recycling line 33 and a cathode recycling line 34 are respectively formed on the anode electrode 2 and the cathode electrode 3. An inert gas feeding line 20 and a steam feeding line 40 are connected to the anode recycling line 33 and the cathode recycling line 34 respectively. Detection means 24, 26 for measuring temperature and stream partial pressure are provided on the anode electrode 2 or the cathode electrode 3, respectively. Gas feeding adjustment valves 21, 23 or stream feeding adjustment valves 41, 43 for controlling the steam partial pressure of the anode electrode 2 or the cathode electrode 3, respectively, to a predetermined value based on the results of the measurements by means of the abovementioned detectors, are provided on the inert gas feeding line 20 and the steam feeding line 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid fuel cell power plant, and more particularly to a phosphoric acid fuel cell capable of controlling a change in phosphoric acid volume in a fuel cell body during start-up / shutdown operations. Related to power plants.

[0002]

2. Description of the Related Art Conventionally, a fuel cell has been known as a device for directly and directly converting chemical energy of fuel such as coal or petroleum into electric energy under isothermal conditions. In this fuel cell, usually, a pair of porous electrodes sandwiches a matrix containing an electrolyte, a fuel gas such as hydrogen is brought into contact with the back surface of one electrode, and an oxidant such as air is placed on the back surface of the other electrode. When they are brought into contact with each other, electric energy generated by the electrochemical reaction that occurs at this time is taken out from between the electrodes. In this case, hydrogen or a reformed gas obtained by reforming natural gas is used as the fuel gas, and air or oxygen is used as the oxidant. As the electrolyte, a molten carbonate, an alkaline solution, an acidic solution, a solid polymer, a solid oxide, or the like is used. Recently, a phosphoric acid fuel cell using phosphoric acid as an electrolyte has been attracting attention.

FIG. 2 shows a schematic structure of a conventional phosphoric acid fuel cell power plant. In the figure, the unit cell of the fuel cell body 1 is a matrix in which an anode electrode 2 having a back surface in contact with a fuel such as hydrogen and a cathode electrode 3 having a back surface in contact with an oxidant such as oxygen are impregnated with an electrolyte. It is configured by arranging it on both sides with sandwiching. A plurality of the unit cells are alternately stacked via the gas separation plate to form the fuel cell body 1.

Natural gas 4 and steam 5 in the reformer 6
The mixed gas of and is converted into a hydrogen-rich gas by a steam reforming reaction, the hydrogen-rich gas is supplied to the anode electrode 2, and the compressed air 7 is supplied to the cathode electrode 3. The hydrogen-rich gas supplied to the anode electrode 2 electrochemically reacts with the compressed air 7 supplied to the cathode electrode 3 to become air, water and heat.

The gas discharged from the anode electrode 2 is discharged to the atmosphere 11 through the anode outlet phosphoric acid adsorber 8, the anode outlet condenser 9 and the reformer burner 10. The gas discharged from the cathode electrode 3 is fed to the cathode outlet phosphoric acid adsorber 12,
It is discharged to the atmosphere via the cathode outlet condenser 13 and the reformer burner 10. The gas in the anode electrode 2 and the cathode electrode 3 is circulated from the outlet line of each electrode to the inlet line by the anode recycle blower 14 and the cathode recycle blower 15 provided in the anode recycle line 33 and the cathode recycle line 34, respectively, and Used. In addition, 16, 17, and 18 are
These are an anode fuel supply valve, a cathode air supply valve and an atmosphere shutoff valve, respectively.

Further, the phosphoric acid type fuel cell is operated at 20
Since the temperature becomes a high temperature of about 0 ° C. and the temperature is kept at 50 ° C. at the time of stop, it is not shown in FIG. Cooling water is being supplied. Therefore, the temperature of the fuel cell main body 1 is controlled by raising and lowering the temperature of the cooling water during the start and stop operations.

[0007]

By the way, the anode electrode 2 and the cathode electrode 3, and further, the matrix sandwiched between them is a porous body, in which a large amount of phosphoric acid is stored. This phosphoric acid has a function as an electrolyte and a sealing function to prevent direct contact and mixing of fuel and oxidant, but it reaches equilibrium depending on temperature and its concentration (temperature and water vapor partial pressure). ) Has the property of changing the volume. Therefore, there occurs a phenomenon that the phosphoric acid volume also changes due to the temperature change of the fuel cell main body 1 accompanying the start / stop operation of the fuel cell power plant.

When the volume of phosphoric acid changes in this way, the phosphoric acid filled in the porous anode electrode 2, cathode electrode 3 and matrix overflows around the electrodes,
As a result, the conductivity is lowered due to the ions due to the defective shield function and the decrease in the electrolyte, thereby shortening the battery life. Also, when phosphoric acid leaks out of the unit cell, it drips down the laminated surface of the fuel cell body 1 and a liquid junction occurs between the fuel cell body 1 and the gas supply and discharge lines of the anode electrode and the cathode electrode. , There is a risk of causing serious trouble due to poor insulation.

Further, the anode electrode 2 and the cathode electrode 3 are gas diffusion electrodes made of a porous material, and a catalyst layer is formed on the surface in contact with the matrix. in this case,
Since the fuel and the oxidant gas diffuse into the pores of the porous body and move to the catalyst layer, in general, phosphoric acid is contained in the porous portions of the anode electrode 2 and the cathode electrode 3 to the extent that gas diffusion is not hindered. It is designed to be filled. However, due to the temperature change of the fuel cell main body 1 accompanying the start / stop operation of the fuel cell power plant, the phosphoric acid moves due to the phosphoric acid volume change, and the pores of the porous body including the catalyst layer described above are generated. A phenomenon (flooding phenomenon) in which phosphoric acid of a predetermined value or more stays occurs. As a result, there is a problem that the battery characteristics are deteriorated due to the poor gas diffusion of the fuel and the oxidant with the start / stop operation, and the life of the battery is shortened.

The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and its object is to minimize changes in the phosphoric acid volume of the fuel cell body during start-up and stop operations. It is to provide a fuel cell power generation plant capable of performing the above.

[0011]

In order to achieve the above object, the phosphoric acid fuel cell power plant according to claim 1 introduces a fuel and an oxidant to an anode electrode and a cathode electrode, respectively, and an outlet of the anode electrode. In the fuel cell power plant having an anode recycle line and a cathode recycle line that circulate from the line and the outlet line of the cathode electrode to the inlet line of the anode electrode and the inlet line of the cathode electrode, respectively, in the anode recycle line and the cathode recycle line, An inert gas supply line is connected to at least one side, and an anode electrode or a cathode electrode having a recycling line connected to the inert gas supply line is provided with a detector for measuring the temperature and the partial pressure of water vapor. , The inert gas supply line The, based on the measurement result of the detector, characterized in that the gas supply regulation valve for controlling the water vapor partial pressure of the anode electrode or the cathode electrode to a predetermined value is provided.

According to another aspect of the phosphoric acid fuel cell power generation plant of the present invention, a fuel and an oxidant are introduced to an anode electrode and a cathode electrode, respectively, and an anode recycle line is circulated to an outlet line of the anode electrode and an inlet line of the cathode electrode. In a fuel cell power plant having a cathode recycle line, a steam supply line is connected to at least one of the anode recycle line and the cathode recycle line, and the anode electrode or the cathode electrode having a recycle line connected to the steam recycle line is A detector for measuring the temperature and the steam partial pressure is provided, and the steam supply line is provided with a steam supply control valve for controlling the steam partial pressure to a predetermined value based on the measurement result of the detector. It is characterized by

[0013]

In the phosphoric acid fuel cell power plant of the present invention having the above-mentioned structure, the circulation operation by the recycle blower operation is carried out in at least one of the anode recycle line and the cathode recycle line during the start / stop operation. To do. At this time, for at least one of the anode electrode and the cathode electrode, the temperature and the water vapor partial pressure are detected by the detection means, and the water vapor partial pressure of the anode electrode or the cathode electrode is controlled to a predetermined value by the command of the detection means. In addition, an inert gas supply control valve provided in the inert gas supply line or a steam supply control valve provided in the steam supply line is controlled. As a result, the phosphoric acid volume in the fuel cell body can be controlled to a predetermined value even during the start / stop operation.

[0014]

【Example】

(1) Configuration of Representative Embodiment One embodiment of the present invention will be specifically described below with reference to FIG. The same parts as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, 20 is the anode electrode 2.
An anode inert gas supply line (for example, N ₂ gas supply line) connected to the inside of the anode recycling line on the inlet side of the anode inert gas supply control valve 2
1 is arranged. 22 is a cathode inert gas supply line (for example, N ₂ gas supply line) connected to the inside of the cathode recycling line on the inlet side of the cathode electrode 3.
The cathode inert gas supply control valve 23 is arranged here.

Reference numeral 40 is an anode steam supply line connected to the inside of the anode recycling line on the inlet side of the anode electrode 2, and an anode steam supply control valve 41 is arranged therein. Reference numeral 42 denotes a cathode steam supply line connected to the inside of the cathode recycle line on the inlet side of the cathode electrode 3, where the cathode steam supply control valve 4 is provided.
3 are arranged.

The anode electrode 2 is provided with a detecting means 24 for measuring its temperature and water vapor partial pressure. The output end of the detection means 24 for measuring the temperature and the steam partial pressure is connected to the anode inert gas supply control valve 21 and the anode steam supply control valve 41 according to the detected temperature and the steam partial pressure.
It is connected to the arithmetic and control unit 25 which controls the valve opening degree. The cathode electrode 3 is also provided with a detection means 26 for measuring the temperature and the water vapor partial pressure, and the output end of the detection means 26 for measuring the temperature and the water vapor partial pressure, according to the detected temperature and the water vapor partial pressure, It is connected to an arithmetic and control unit 25 which controls the valve openings of the cathode inert gas supply control valve 23 and the cathode steam supply control valve 43.

(2) Operation of Representative Embodiment In the phosphoric acid fuel cell power generation plant of the present invention having the above-mentioned structure, during the temperature raising / lowering operation of the fuel cell body 1 at the time of start / stop operation, Anode recycling blower 1
4 and the cathode recycle blower 15 are driven.
At this time, since the anode recycle line 33 and the cathode recycle line 34 are in a pressure-holding state of nitrogen gas, the nitrogen gas is uniformly supplied to the anode electrodes 2 and the cathode electrodes 3 of the unit cells stacked on the fuel cell body 1, and the stirring is performed. Circulation operation is carried out. At the same time, the temperatures and the water vapor partial pressures of the anode electrode 2 and the cathode electrode 3 are detected by the detection means 24 and 26, respectively, and the outputs thereof are the arithmetic and control unit 2.
5 is sent.

By the way, the specific gravity of phosphoric acid is determined by temperature and phosphoric acid concentration, as shown in the following equation (1). (References: Farr, TVA Chem. Eng. Report.
tNo. 8, P-44 1950 issued)

## EQU1 ## p = f (T, W) (1) where p: specific gravity of phosphoric acid (g / cm3) T: phosphoric acid temperature (° C.) W: phosphoric acid concentration (weight ratio) (-) The phosphoric acid concentration W is determined by the phosphoric acid temperature and the water vapor partial pressure as shown in the following formula (2). (Reference: "Va
por Pressure of Phosphori
c Acids. "Author: EARL.H.BROWN
etc)

## EQU2 ## W = f (T, P _H2O ) ... (2) where P _H2O : steam partial pressure (mmHg) On the other hand, as described above, the phosphoric acid volume during the power generation test is
Since it changes with the start / stop operation, problems such as leakage of phosphoric acid to the outside of the unit cell and flooding phenomenon of the gas diffusion electrode may occur. Maintaining volume is desirable.

From the above, the optimum phosphoric acid volume during the start-stop operation is determined by the following formula.

[0021]

## EQU00003 ## Phosphoric acid volume during start / stop operation / phosphoric acid volume during power generation operation =
{1 / (P _{ON / OFF} * W _{ON / OFF} )} / {1 / (P _OPER * W
_OPER )} (3) where P _{ON / OFF} : Specific gravity of phosphoric acid under start _/ stop operating conditions W _{ON / OFF} : Concentration of phosphoric acid under start _/ stop operating conditions (weight ratio) P _OPER : Specific gravity of phosphoric acid during power generation operation W _OPER : Phosphoric acid concentration during power generation (weight ratio) In formula (3), phosphoric acid volume during power generation 1 / (P _OPER *
W _OPER ) is calculated by using the formulas (1) and (2) according to the power generation conditions of the fuel cell power generation plant (power generation temperature T, supply gas flow rate and gas temperature of anode electrode and cathode electrode, cell current). .

Here, in the arithmetic and control unit 25, at the detected temperature T of the anode electrode and the cathode electrode, (3)
The optimum water vapor partial pressure P _H2O (optimum) that satisfies the equation is calculated from the equations (1) and (2). Further, the arithmetic and control unit and 25 detect the detected water vapor partial pressure P _H2O of the anode electrode and the cathode electrode and the optimum water vapor partial pressure P _H2O (optimum
), The anode inert gas supply control valve 21, the anode steam supply control valve 41, the cathode inert gas supply control valve 23, and the cathode steam supply control valve 43.
Give a command to. The above operation is performed not only during the start / stop operation of the fuel cell power plant, but also during the heat insulation state (about 50 ° C.) of the fuel cell main body 1 during the stop of the fuel cell power plant.

In the present embodiment having the above-described structure, the anode electrode 2 and the cathode electrode are provided when the fuel cell main body is in the temperature rising / falling state at the time of the start / stop operation or in the heat retaining state during the stop. The temperature and water vapor partial pressure of No. 3 are measured by the detection means 24 and 26, and the arithmetic and control unit 25 which receives the output of the detection result calculates the phosphoric acid volume in the fuel cell main body, and the value is a predetermined value. If they are different, by giving a command to the inert gas supply control valve 21 or the steam supply control valve 41, the anode electrode and the cathode electrode can be controlled to have a predetermined steam partial pressure corresponding to their temperatures. As a result, the phosphoric acid volume of the fuel cell main body during the start-stop operation or during the stop can be continuously controlled to a predetermined value, for example, the phosphoric acid volume value during the power generation operation. It is possible to prevent the leakage of phosphoric acid to the outside of the cell due to a change in the phosphoric acid volume, prevent the sealing function from failing, and prevent the ion conductivity from decreasing due to a decrease in the electrolyte, thereby extending the life of the fuel cell. it can. Furthermore,
It is possible to suppress the flooding phenomenon caused by the phosphoric acid transfer caused by the change in the phosphoric acid volume, and to extend the life of the fuel cell characteristics.

(3) Other Embodiments The present invention is not limited to the above embodiments, and even if a means for controlling the partial pressure of water vapor is provided only on either the anode electrode or the cathode electrode, the present invention is compared with the prior art. It is possible to exert a superior effect. It is also possible to adjust the water vapor partial pressure using only one of the inert gas supply control valve and the steam supply control valve. Further, the means for controlling the inert gas supply control valve or the steam supply control valve based on the detected temperature or water vapor partial pressure does not necessarily need to be a computing device, and is simply a solenoid valve that operates according to the detected value. May be used.

[0025]

As described above, according to the present invention, the volume of phosphoric acid in the fuel cell body can be controlled to a predetermined value, for example, the volume of phosphoric acid during power generation operation even during the start-stop operation, so that the volume of phosphoric acid changes. It is possible to prevent the leakage of phosphoric acid to the outside of the cell due to the above, prevent the deterioration of the sealing function due to it, and prevent the deterioration of the ionic conductivity due to the decrease of the electrolyte, thereby prolonging the life of the fuel cell. Further, it is possible to suppress the flooding phenomenon caused by the phosphoric acid transfer caused by the change in the phosphoric acid volume, and to extend the life of the fuel cell characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a phosphoric acid fuel cell power generation plant of the present invention.

FIG. 2 is a block diagram showing an example of a conventional phosphoric acid fuel cell power generation plant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fuel cell main body 2 ... Anode electrode 3 ... Cathode electrode 20 ... Anode inert gas supply line 21 ... Anode inert gas supply control valve 22 ... Cathode inert gas supply line 23 ... Cathode inert gas supply control valve 24, 26 Temperature / steam partial pressure detecting means 25 Computational control device 40 Anode steam supply line 41 Anode steam supply control valve 42 Cathode steam supply line 43 Cathode steam supply control valve

Claims (2)

[Claims] 1. A fuel and an oxidant are introduced to an anode electrode and a cathode electrode, respectively, and are circulated from an outlet line of the anode electrode and an outlet line of the cathode electrode to an inlet line of the anode electrode and an inlet line of the cathode electrode, respectively. In a phosphoric acid fuel cell power plant having an anode recycle line and a cathode recycle line, an inert gas supply line is connected to at least one of the anode recycle line and the cathode recycle line, and the inert gas supply line is connected. The anode electrode or cathode electrode having a recycling line
A detection means for measuring the temperature and the water vapor partial pressure is provided, and the inert gas supply line is a gas for controlling the water vapor partial pressure of the anode electrode or the cathode electrode to a predetermined value based on the measurement result of the detection means. A phosphoric acid fuel cell power plant comprising a supply control valve. 2. A phosphoric acid fuel cell power generation system having a fuel recycling line and a cathode recycling line for introducing a fuel and an oxidant to an anode electrode and a cathode electrode, respectively, and circulating the fuel gas and the oxidant to the outlet line of the anode electrode and the inlet line of the cathode electrode. In the plant, a steam supply line is connected to at least one of the anode recycle line and the cathode recycle line, and the temperature and the steam partial pressure are applied to the anode electrode or the cathode electrode having the recycle line to which the steam supply line is connected. A detection unit for measuring is provided, and the steam supply line is provided with a steam supply control valve for controlling the partial pressure of steam to a predetermined value based on the measurement result of the detection unit. Fuel cell power plant.